In DC-DC conversion controllers are generally compensated for the purposes of stability and regulation.
A typical DC-DC converter arrangement is shown in FIG. 1.
The DC-DC converter arrangement comprises a switchable power stage 11, wherein an output voltage is generated according to a switching signal and an input voltage. The switching signal is generated in a digital controller 16 that adjusts the output voltage to a reference voltage. The driver 17 translates the switching signal to individual switching signals for the high-side switch 12 and the low side-side switch 13. The switchable power stage further comprises an inductor 14 shown in terms of inductance and equivalent series resistance and a capacitor 15 shown in terms of its capacitance and equivalent series resistance (ESR). During a charge phase, the high-side switch is turned on and the low-side switch is turned off by the switching signal to charge the capacitor. During a discharge phase the high-side switch is turned off and the low-side switch is turned on to match the average inductor current to the load current.
The switching signal may be generated as digital pulse width modulation (PWM) signal with a duty cycle determined by a control law. The controller 16 may be employ analogue or digital compensation schemes when operating in PWM.
Controllers that employ analogue compensators typically rely on compensation networks that are fixed using resistors and capacitors connected to the controller IC pins as shown in FIG. 2 where an output voltage VOUT is compared to a reference voltage VREFERENCE by comparator 21 to generate an error voltage VCOMP. Sometimes the compensation components are internal to the IC.
In DC-DC POL modules, a tuneable-loop concept has been developed as disclosed in U.S. Pat. No. 7,432,692, 2008 to allow variation of the loop compensation by attaching resistors and capacitors to the pins of the module to override the compensation the module manufacturer has configured internally. Determining suitable values for the external components is typically performed by the module user by way of tables or formulae.
Controllers that employ digital compensators as shown in FIG. 3 typically use a graphical user interface (GUI) and communication bus 18 (FIG. 2) to calculate suitable compensation parameters and communicate those values to the controller IC which then may be stored into non-volatile memory 19 (FIG. 2).
However, module end users may not have the required communication bus at their disposal or may not desire to utilise the GUI because of the complexity of such a task. Adaptive controllers may be employed to obviate this need, but the frequency and phase characteristics of the final system after adaptive control compensation has converged can be unpredictable and therefore the response cannot be pre-determined to any suitable degree of certainty.
Furthermore, control methods may adopt different modes in which the selected coefficients change according to the mode of operation. Typically, adaptive controllers perform poorly in this situation because the learning of the adaptive loop is disrupted by the mode changes
As mentioned, in DC-DC conversion controllers are generally compensated for the purposes of stability and regulation. However, the requirement to design a robust controller that is stable over all power stage parameter values and conditions is at odds with the requirement to maximize regulation performance. It is especially difficult in the case of DC-DC POL modules to determine and select a suitable compensator because                a) the output capacitance of the end user is typically not well defined when the module manufacturer determines the compensation and        b) the end user has limited means or skill in determining and configuring the correct compensation once the output capacitance is well defined.        
Therefore what is required is a compensator for a power converter that is easy to configure and optimally regulates.